The present invention is related to swimming flippers comprising a blade of flexible and relatively rigid material, and a shoe of relatively soft and elastically extensible material associated to one end of the blade.
In the swimming flippers presently produced the shoe, be it either formed with a complete shape or open rearwardly and provided with a strap (for the rear holding of the foot and for the length adjustment of the housing thereof), is rigid with the blade, or in any case is permanently assembled thereto by means of mechanical systems allowing assembly and disassembly of the two parts only with the aid of suitable tools, and in any case not when the shoe is worn on the user's foot.
For the manufacturing of flippers of the above-referenced type, long since discontinued the production methods consisted of the simultaneously moulding in a single mould of curable rubbers of different hardness. The manufacture technology has by now been consolidated, comprising initially the injection moulding of the blade, employing a rigid and flexible thermoplastic material having a low melting point, normally E.V.A. (Ethylene Vinyl Acetate) or rigid polyurethane or other polymers. Thereafter, on the rear end of the blade so formed the shoe is overmoulded, for which is normally employed a thermoplastic rubber having chemical affinity with the thermoplastic material of the blade and a higher melting temperature, so that it can be welded to the blade due to a chemical-thermal effect.
A technology more frequently adopted for specialized uses of the flipper (agonistic flipper-swimming, deep sea diving) consists of a moulded shoe of generally natural rubber, sometimes a thermoplastic rubber, and a blade of rigid and flexible material coupled and fixed therebetween by means of mechanical systems, normally by screws. This type of connection, which can be disconnected only with the aid of proper tools, also leads to flippers which, both from the point of view of the user and during operation, must be considered as "monolithic", even if uncoupling of the two parts is allowed for the purpose of replacement.
These monolithic flippers have several drawbacks, summarized in the following.
a) Firstly, the monolithic flippers involve several difficulties and inconveniences in connection with wearing and removing, for which the user is obliged to intervene manually, frequently with both hands, either for inserting or for withdrawing the foot relative to the flipper. It is also to be considered that, in case of use for scuba diving, these operations are performed by the completely dressed diver, i.e. wearing a diving suit, weights, breathing apparatus, diving jacket, with precarious equilibrium conditions, on the sea shore or within the waves of the water line, on the deck of a rolling boat or below the ramp of the boat itself. On the other hand the flipper must be worn and removed when going in and out the water, since walking on flippers is almost impossible and anyway dangerous.
b) In the case of rearwardly open shoes provided with a strap for the back holding of the foot, the obstacle determined both by the shoe length, and by the tails of the strap projecting laterally, as well as by the large buckles for connecting and adjusting the strap, originates an appreciable hydrodynamic resistance which limits in use the efficiency of the flipper motion. As far as the length of the rearwardly open shoes is concerned, same is due to the fact that such shoes are not worn on the bare foot or possibly on a thin protective socking, but on an ankle-boot made of neoprene or similar materials, having a rubber anti-slip sole, which is per se particularly thick. This ankle-boot accomplishes both the ambulation function, and the thermal protection task: use thereof is normally widespread, but involves relevant problems of hydrodynamics and of connection solidity between foot and flipper.
In more remote times, when the moulding technologies and the available materials did not enable overmoulding a relatively soft material (that of the shoe) on a relatively rigid material (that of the blade), in order to obtain sufficiently differentiated characteristics of rigidity or elasticity, not obtainable with a monolithic structure of the flipper, it had been proposed to manufacture the shoe and the blade as distinct elements, assembled to each other mechanically with mutual restrained-joint systems.
Examples of these solutions are disclosed in Italian patents n. 709845, n. 799797 and n. 801541.
These solutions contemplated lateral members of mutual fitting, placed on the sides of the shoe and of the blade, adapted to be fixedly joined with each other and to be disassembled by means of approaching and, respectively, departing the two parts along a direction parallel to the plane of the blade, i.e. in a forward-rearward direction. These operations involved the application of a huge thrust force (or of a traction force, respectively), with a relevant manual effort, normally with the aid of suitable tools, and not without engagement and disengagement difficulties of the parts for the mutual restrained-joint.
Such solutions, which evidently did solve the problem of making the shoe and the blade by different materials, were only directed to the manufacturers, certainly not to the users. Actually:
a) the separation and union of the two flipper components would have required for the user still more uncomfortable, difficult and hard wearing and removing operations with respect to the monolithic flippers, and thus not practicable;
b) these flippers did not afford any advantage connection with the hydrodynamic friction: on the contrary, the restrained joint members did increase the plan width thereof;
c) such flippers didn't lead to the achievement of any advantages either with respect to the solidity of connection between foot and blade: the shoe was normally loose and slack, and moreover the blade was fitted only in the forward half of the shoe, thus allowing under effort a foot flexion which strained the leg and considerably reduced the swimming efficiency.